The present invention relates to a method for producing silicon tip field emitter arrays, and more particularly, to a method for producing silicon tip field emitter arrays of micro-triodes by using the oxidized porous silicon layer of a silicon substrate.
Recently, there have been some attention focused on micro-triodes having the same functions as conventional triodes. A field emitter array of micro-triodes is fabricated by combining emitter tips made by micro-treating a silicon substrate with corresponding gate electrodes and anodes in order to be operated in a vacuum state. The diameter of the tip apex ranges from several tens angstrom to several thousands angstrom.
Such micro-triode consists of an emitter tip of 1.about.2 .mu.m in height, with a gap of 0.5.about.1.0 .mu.m between the tip and the gate and a gap of 100.about.500 .mu.m between the gate and the anode glass. Accordingly, the micro-triode can be formed into a thin film shaped structure.
The micro-triode may be used as an amplifier in a micro-wave region or as a switching means, and a high frequency power module can be made by combining numerous micro-triodes to an array. Also, a display panel can be constructed by combining such an array and an anode made by depositing phosphor compounds on the thin transparent film electrode (R. Meyer, "Recent Development on Microtips Display at LETI", Technical Digest of IVMC, page 6.about.9, 1991). The display panel can be used as a screen for portable televisions or computer monitors since it is a thin plate less than one centimeter in thickness, and also as a large flat panel screen for HDTV in the future. It is also known that the tip arrays can be applied to sensors for measuring pressure, magnetic fields and vacuums (Juniji Itoh, et al., "Fabrication of Lateral Triode with Comb-shaped Field-Emitter Arrays", Technical Digest of IVMC, page 99.about.100, 1993).
The cathode tips and the gates of the above micro-triodes can be fabricated by the following conventional method.
First, a silicon dioxide(SiO.sub.2) pattern is formed on a silicon substrate by the lithography process and then the silicon substrate is etched to a thickness of 7,000.about.15,000.ANG.. A thermal oxide layer is then formed over the entire surface of the silicon substrate.
Next, a silicon oxide layer and a gate metal layer are sequentially deposited by using an electron beam evaporator and then a cathode tip is formed by lifting-off the portion over the cathode tip (Keiichi Betsui, "Fabrication and Characteristics of Si Field Emitter Arrays", Technical Digest of IVMC, page 26-29, 1993).
Though the conventional lift-off process appears to be a simple one, it has some disadvantages. First, the configurations of the regions surrounding the cathode tips are not entirely uniform since the silicon oxide layer and the gate metal layer thereon are formed mainly by directional deposition using an electron beam evaporator and, thus, such lack of uniformity of the configurations results in uneveness of the array's operation.
Second, the height of the cathode tip relative to the gate is difficult to control because they are dependent on the etched depth of the silicon substrate and the thickness of the silicon oxide layer.
Third, the quality of the silicon oxide layers formed by the electron beam evaporator differs depending on the processing conditions such as the vaccum state, and the temperature of the silicon substrate. These process conditions make it difficult to obtain products of desired specifications during the subsequent processes.